As far as how useful Jira is, a huge percentage of that is going to be your team's processes external to Jira. I have found it to be a very good mirror. If your team's processes are a mess, your Jira instance will quickly become one as well. But if your team is organized and is bringing an existing, functional system to Jira, I have found that it's a good enough value add to be worth it.
It's definitely an enabler, though, rather than a tool that will funnel you into good practices. (The same can be said for Confluence but it's even more true there IMO.)
One light at the end of the tunnel is the Mac app (for some reason there is no Windows or Linux version). It's much more lightweight and feels way faster than the web version. However, it is buggy in my experience, and a fair few things I do a lot can't be done in it and require the web interface, but for quickly checking stuff it mostly works.
The performance is absolute dog shit. Every interaction with it painfully slow. For example, the page to view a single issue is almost 20MB fetched over 100 HTTP requests and takes 10 seconds to load. This is without cache. With assets cached, it is still 4 seconds to render. This is the fastest interaction by the way. Everything else is worse.
Maybe some of this is my organization's fault. I really don't know. What I do know is that it is so slow that I dread every interaction with it.